Device for error recognition in a digital signal evaluation unit

ABSTRACT

A device for signal evaluation is described, in particular for knock recognition in an internal combustion engine, in which the signals forwarded by sensors are evaluated digitally and error recognition is carried out that performs two different test functions, whereby a first test function supplies a test pulse at a specifiable location, and the second test function clears the sensor signals, and the reaction of both the analog and digital parts of the circuit are monitored.

[0001] The invention concerns a device for error detection in a digitalsignal evaluation unit according to the general class of the main claim.

BACKGROUND OF THE INVENTION

[0002] It is known that, in signal evaluation units designed as analogevaluation IC's, for example, monitoring measures are required thatallow misoperations to be recognized. Various possibilities foraccomplishing this are known. For example, a method for monitoring anderror recognition is presented in DE-P 197 560 81.4 that is carried outin an analog evaluation IC in conjunction with knock detection in aninternal combustion engine. With this knock detection, thestructure-borne noise signals supplied by the knock sensors areforwarded to the evaluation IC via a multiplexer. This IC is composed,at the least, of an amplifier, a filter, a rectifier, and an integrator.The resultant integrator result is used as the result of knock detectionin order to calculate a knock index for the knock control. Signalevaluation takes place in this IC in analog form. Two test options areimplemented to monitor the operatability of the integrated circuit (IC).These test options are referred to as test pulse and zero test. Usingthis type of diagnosis, the entire signal path except for themultiplexer can be checked for operatability.

[0003] In the first test option-the test pulse-a test signal is suppliedto the evaluation chain after the multiplexer. The downstream integratoris fully modulated by means of this signal in a relatively short periodof time, independently of the amplifier level setting. If it isrecognized that the expected full modulation of the integrator has notoccurred after a relatively short period of time, an error is detected.In the second test option-the O-test-the signal path is separated afterthe multiplexer. In this case, only the disturbing noises, e.g.,background noises, occurring internally in the integrated circuit (IC)are integrated in the integrator. The signal available in the integratorthen provides information as to whether erroneous disturbances haveoccurred, or if any other misoperations are present. The integratedcircuit for evaluation of knock signals in an internal combustion enginemust be monitored, since, if the evaluation circuit would fail,erroneous values for knock control would be provided and the knockcontrol itself would no longer function correctly, and damage couldoccur to the internal combustion engine.

[0004] New units for signal evaluation, e.g., in conjunction with knockdetection in internal combustion engines, have digital evaluation IC's.The entire signal evaluation, if possible, is thereby performed with theaid of a digital arithmetic and logic unit. Such an evaluation ICdesigned to evaluate the output signals of knock sensors is described inpatent application DE-P 100 041 66.3. In this type of digital signalevaluation, a typical property, e.g., components typical for knock, areextracted from the conditioned and digitized output signals from thesensors, and they are compared with specifiable threshold values forknock detection. A checking or monitoring of the operatability of the ICis not performed in this digital signal evaluation described in DE-P 100041 66.3.

OBJECT OF THE INVENTION

[0005] The object of the invention is to perform reliable errordetection in a digital signal evaluation, e.g., knock detection, with adigital evaluation IC, whereby the errors that may occur in the entireevaluation path of the digital evaluation IC should be reliablydetected.

ADVANTAGES OF THE INVENTION

[0006] The device, according to the invention, for error detection in adigital signal evaluation having the features of claim 1 has theadvantage that errors and/or misoperations are reliably detected andthat the flexible adaptations made possible with the digital realizationof the signal evaluation unit can be retained. Using the proposeddiagnoses, it is possible to monitor the digital and analog parts of theentire evaluation unit, in particular those of the evaluation IC.

[0007] These advantages are attained by means of a device for errorrecognition in a digital signal evaluation having the features of claim1, in which two test functions are evaluated for error recognition, andthe reaction of the evaluation unit to these test functions is checked.

[0008] Further advantages of the invention are attained by means of themeasures indicated in the dependent claims. Particularly advantageousfor their use in conjunction with knock detection in an internalcombustion engine is the fact that the control logic for the methodaccording to the invention is advantageously implemented in the computerof the electronic control unit of the internal combustion engine.

DRAWING

[0009] An exemplary embodiment of the invention is presented in the soleFIGURE in the drawing, and it is explained in greater detail in thesubsequent description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The exemplary embodiment of the invention presented in the FIGUREis shown as an example of the evaluation of output signals from twoknock sensors 10 and 11, each of which is associated with one cylinderof a not-further-shown internal combustion engine 9. Each of the outputsignals S1 and S2 of the knock sensors 10 and 11 is forwarded to asignal conditioning circuit 12, 13, where they are conditioned by saidsignal conditioning circuit in such a fashion that they can be forwardedby the multiplexer 14 in a specifiable fashion.

[0011] The multiplexer 14 and a filter 15, e.g., an antialiasing filter,a downstream amplifier 16, and an analog/digital converter 17 form theanalog part 18 of the initial conditioning of input signals. The actualinitial conditioning of input signals takes place in the digital part19, which is adjacent to the analog part. For this purpose, thesignal-which is a digital signal, not shown in drawing SD—supplied bythe analog/digital converter 17 is forwarded to the digital part 19.

[0012] The digital signal evaluation and/or the digital part 19 arepresented as examples for three different exemplary embodiments. On theone hand, the digital part 19 can include a filter 20, a rectifier 21,and an integrator 22, or it can include means for performing a discreteFourier transformation 23, or means for performing a fast Fouriertransformation (FFT) 24. Which one of the signal evaluations performeddepends on specifiable particularities and can be adapted to theavailable signals SD, or they can be selected in project-specificfashion. The evaluation signal SA that includes the knock indices occursat the outlet of the digital signal evaluation 19. Based on these knockindices, knocks are then recognized in block 25, e.g., a comparingelement. Block 25 can also be a controller of the electronic controlunit of the internal combustion engine that requires the knock detectionto influence certain variables of the internal combustion engine, suchas ignition. In general, the entire device for knock detection can alsobe a component of the electronic control unit of the internal combustionengine.

[0013] With t0he exemplary embodiment presented in the FIGURE for signalevaluation, a plurality of knock sensors 10,11 can be connected to amultiplexer 14 via symmetrical input circuit elements. Said multiplexeralways connects only that knock sensor that best recognizes thecombustion taking place. The output signal from the multiplexer 14 isthen forwarded to the analog/digital converter 17 via the filter 15,e.g., an antialiasing filter and, if applicable, via an amplifier 16 aswell. Once the signal SD is present in digital form at the outlet of theanalog/digital filter 17, the actual digital signal evaluation can takeplace. This digital signal evaluation, which takes place in the digitalblock 19, typically contains an energy evaluation. In place of an energyevaluation, a peak value determination could also be carried out for thesubsequent knock detection. A possible method for energy evaluation thatis already known in conjunction with an analog circuit described in DE-P197 560 81.4, consists of filtering the signal from the knock sensor,rectifying or squaring the filtered signal and then integrating thesignal. As an alternative, a discrete Fourier transformation (DFT) or afast Fourier transformation (FFT) could be carried out. Each of thethree evaluation methods named makes it possible to evaluate a pluralityof frequency ranges and suppress any interference frequencies that arepresent. As the result of this evaluation, one or more knock indices arethen available per combustion in one cylinder of the internal combustionengine. Knock is detected when this knock index or these knock indicesexceed certain specifiable and, if applicable, adaptable thresholds. Forexample, a reference value for knock-free operation can also be takeninto account in this comparison. Such a reference value can always beobtained with the same evaluation unit when it is ensured thatknock-free operation is present. Knock-free operation occurs under knownoperating conditions of the internal combustion engine. Since the knockdetection according to the invention is used in conjunction with anelectronic control unit for the internal combustion engine thatrecognizes these operating conditions, it is possible to determine theknock values ikr as well as the reference values rkr from the signalsSA.

[0014] Based on the common abbreviations for: Knock value ikr Referencevalue rkr Knock-detection threshold ke

[0015] knock is detected when the following applies:

ikr/rkr >ke

[0016] The above-named condition for knock detection, which is checkedin circuit part 25, for example, is also used in conventionalknock-detection systems. In contrast to the conventional systems,however, signal evaluation and the essential initial conditioning ofinput signals is carried out as digital signal evaluation in thedescribed means of attaining the object of the invention. Knock value,reference value, and knock-detection threshold are all digital values,so that digitization of the signal SA is therefore eliminated.

[0017] The signal evaluation takes place in various frequency ranges,whereby the selection of frequency ranges takes place in such a fashionthat the frequency ranges with a high knock signal portion arepreferred, and those with a high interference portion (interferencefrequencies) are suppressed. The knock values ikr determined forindividual frequencies represent knock indices that, in the end, areevaluated for knock detection.

[0018] According to the invention, a monitoring function that performstwo different tests is used for a digital evaluation unit or a digitalevaluation IC that is developed and functions in the manner described.The monitoring can take place during specifiable monitoring phases. Themonitoring phases are specified, for example, in such a fashion thatthey are activated immediately after the internal combustion engine ispowered-on. It is also possible to schedule the monitoring phases insuch a fashion that they take place under operating conditions at whichknocking is not expected to occur.

[0019] To perform the monitoring, the IC can be operated in two testmodes. In the first test mode—which is also referred to as test pulse—atest signal is supplied at the multiplexer 14. The test signal canthereby be provided at an available inlet of the multiplexer 14, or atan additional inlet that is used only for the test. A filter from theRAM or a filter from a test ROM can be used as the filter for the signalcoming from the multiplexer 14. The test signal is designed so that,when amplification is greatest, the integrator is modulated as far aspossible. The modulation of the integrator 22 also depends on the filterused and the length of the measurement window. The length of themeasurement window is the duration of the test signal, for example.

[0020] The test signal and/or a test pulse TP is self-generated in theevaluation circuit, to the extent possible, but, in one possibleembodiment, it could also be supplied from the outside. The IC isalright when the integrator exceeds a specifiable value. In order torecognize that the IC is alright, the value of the integrator iscompared with a threshold value after a specifiable period of time, forexample, whereby this comparison can take place using a comparator or acomparison operation in the computer. If the integrator value exceedsthe threshold value, the IC is recognized as being alright. If theintegrator value does not exceed the threshold value, however, a displaycan be triggered and/or knock control can be engaged and, if applicable,a switch can be made to emergency operation of the knock control.

[0021] In a second test mode—referred to as the zero test—the inputsignal is cleared at the multiplexer 14, i.e., a signal is not suppliedto the evaluation circuit. In addition to the clearing of the signals,the two inputs of E1 and E2 at the multiplexer 14 can beshort-circuited. The two inputs of one sensor are thereforeshort-circuited as well. A filter from the RAM or the test ROM can beused again as the filter for the signal coming from the multiplexer. TheIC is alright, the 2 inputs of a sensor E1, E2 are short-circuited whenthe integrator result lies below a specificable threshold value. Thecomparison of the integrator contents with this second threshold valueis carried out with the aid of a comparing element (comparator orcomputer function). If an error is detected, a display can be triggeredand/or the knock control can be engaged. The selection of the thresholdvalues can take place with reference to expected integrator values andvaried if necessary.

[0022] The zero test can also be used to perform an offset correctionwhen the interference is too great, in the analog signal path inparticular. The integrator value and/or contents determined in the zerotest are then taken into account in the specification of the zero pointof the digital evaluation circuit.

[0023] Both the digital and the analog part of the evaluation unit canbe checked using the two diagnostic methods. It is thereby determinedwhether the integrated circuit IC of the evaluation unit functionscorrectly. Although the location at which the error occurs (multiplexer14, amplifier 16, etc.) cannot be determined, this is not required,since the information as to whether the IC is fully functional or not issufficient to ensure reliable knock detection and, therefore, reliableknock control.

[0024] The execution of the individual test functions is controlled bymeans, e.g., by the computer of the electronic control unit, that makeit possible to activate the test functions only at specifiable timesand/or if specifiable conditions exist. The monitoring can thereby becarried out during on-going operation, for example, under specifiableconditions, or in the initialization phase and/or in after-run.Recognized errors are displayed and/or saved in fault storage.

[0025] The invention was described with reference to fault monitoring inthe case of a digital evaluation IC for knock detection, but it can alsobe used with other digital IC's. This invention can also be used indigital signal evaluation that is not used (implemented) in a separateIC, but rather directly in a computer of an electronic control unit,e.g., an electronic control unit for an internal combustion engine.

What is claimed is:
 1. A device for signal evaluation having one or moresensors for recognizing a measurement variable, whereby errorrecognition means are available that perform two different testfunctions, wherein the signal processing is designed as digital signalprocessing that evaluates the digitally converted output signal of thesensor or sensors, and the error recognition includes the analog partand the digital part of the device for signal processing.
 2. The devicefor signal evaluation according to claim 1, wherein the device forsignal evaluation has symmetrical inputs to which the sensor or sensorsare connected.
 3. The device for signal evaluation according to claim 1or 2, wherein the sensor or sensors are knock sensors, and knockrecognition is carried out, the result of which is used for knockcontrol.
 4. The device for signal evaluation according to claim 1, 2, or3, wherein it has a multiplexer (14) at the inlet with which the sensorsare interconnected, and wherein, in a first test, a test signal (TP) issupplied at the multiplexer (14) that is selected in such a fashion thatit results in a large modulation at the outlet of the digital signalevaluation, in particular at the integrator
 22. 5. The device for signalevaluation according to claim 4, wherein the test signal (TP) isself-generated in the evaluation circuit.
 6. The device for signalevaluation according to one of the preceding claims, wherein the testsignal (TP) is supplied to the evaluation circuit from the outside. 7.The device for signal evaluation according to one of the precedingclaims, wherein, to perform a zero test, the inputs at the multiplexer(14) are cleared and/or short-circuited, and the integrator value thatthen occurs at the integrator (22) is compared with a specifiable value,and an error is detected when a specifiable value is exceeded.
 8. Thedevice for signal evaluation according to claim 7, wherein the result ofthe zero test is taken into account for offset compensation.
 9. Thedevice for signal evaluation according to one of the preceding claims,wherein means are available that activate the test functions only atspecifiable times and/or when specifiable operating conditions exist.10. The device for signal evaluation according to claim 9, wherein themeans activate monitoring during operation or at specifiable operatingpoints or in the initialization phase and/or in after-run.